Processing StateValues into operands is one of the most costly
parts of instruction selection. As it happens, StateValues are
shared by many nodes, and so we are unecessarily reprocessing
the same StateValues multiple times. This CL introduces caching
for the processed StateValues enabling very fast emitting of
operands for subsiquent instructions with the same StateValue.
The hitrate for the cache is higher than 90% on most optimizations.

BUG=v8:9684

Change-Id: I45db86dcbf22ab972b892f11c608b825aeb3ecf3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2749634Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73342}